Frigid air from the North Pole: What's this polar vortex?

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'Polar vortex' blamed for U.S. deep freeze

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Polar vortex is circulation of strong, upper-level winds that normally surround the North Pole

The distortion can lead to major cold air outbreaks in North America, Europe and Asia

A cold air outbreak caused by the polar vortex is much more widespread than a single storm

Research suggests the distortion could be a side effect of global warming

Americans in two dozen states from the Midwest to the Southeast and Northeast are shivering this week courtesy of a distorted polar vortex. The rush of cold air it's sending southward is the biggest visitor from the North Pole since Santa Claus. The gifts it brings, however, are chilling and generally unwelcome. Much of the United States has plunged into a deep freeze from record low temperatures.

CNN International senior meteorologist Brandon Miller answers a few pressing questions about this phenomenon.

What is a polar vortex? What distinguishes it?

The polar vortex, as it sounds, is circulation of strong, upper-level winds that normally surround the northern pole in a counterclockwise direction -- a polar low-pressure system. These winds tend to keep the bitter cold air locked in the Arctic regions of the Northern Hemisphere. It is not a single storm. On occasion, this vortex can become distorted and dip much farther south than you would normally find it, allowing cold air to spill southward.

How frequently does this polar vortex distortion occur?

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Winter weather grips U.S. – Snow and ice blanket downtown St. Louis and the Mississippi River on Wednesday, January 8.

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Winter weather grips U.S. – People wait outside the Broadway Theatre in New York City to buy tickets for the show "Cinderella" on January 8.

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Winter weather grips U.S. – Water dripping from a New York City subway station freezes on a traffic cone January 8.

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Winter weather grips U.S. – A man walks past a car in Baltimore that is partially covered in ice January 8.

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Winter weather grips U.S. – Ice collects on the Delaware River near Philadelphia on January 8.

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Winter weather grips U.S. – Icicles hang from the bumper of a vehicle in Fort Walton Beach, Florida, on Tuesday, January 7.

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Winter weather grips U.S. – A vehicle drives through a barely visible intersection in Stafford, New York, on January 7.

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Winter weather grips U.S. – Plants covered in ice are seen in Panama City Beach, Florida, on January 7.

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Winter weather grips U.S. – Ice in the Mississippi River flows past the Gateway Arch in St. Louis on January 7.

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Winter weather grips U.S. – Ice forms around rocks on the Brooklyn waterfront, across from Lower Manhattan, on January 7, in New York City.

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Winter weather grips U.S. – A woman braves the cold in Scranton, Pennsylvania, on January 7.

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Winter weather grips U.S. – Passengers wait for a train to arrive in Chicago on January 7, when temperatures were below zero.

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Winter weather grips U.S. – A man clenches his fists while walking past a steam vent in New York City on January 7.

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Winter weather grips U.S. – A man bundles up against the cold in New York City on January 7.

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Winter weather grips U.S. – A couple walks past an advertisement in Pittsburgh during sub-zero temperatures January 7.

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Winter weather grips U.S. – A woman tries to stay warm while waiting for a bus in Brooklyn, New York, on January 7.

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Winter weather grips U.S. – Ice builds up along Lake Michigan at Chicago's North Avenue Beach on Monday, January 6.

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Winter weather grips U.S. – With temperatures nearing 0 degrees, a cloud of steam from a manhole blows across an intersection in downtown Pittsburgh on January 6.

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Winter weather grips U.S. – Men battle the bitter wind as they walk in Chicago on January 6.

Winter weather grips U.S. – Vehicles drive down a snow-covered road in Burton, Michigan, on January 6.

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Winter weather grips U.S. – Metra employees in Chicago walk around LaSalle Street Station on January 6.

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Winter weather grips U.S. – A man warms his hand while running errands in Flint, Michigan, on January 6.

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Winter weather grips U.S. – A commuter walks past warming lamps at a Chicago train station on January 6.

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Winter weather grips U.S. – A woman props up her feet on her luggage January 6 after her flight home was canceled at Logan International Airport in Boston.

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Winter weather grips U.S. – A woman makes her way through a snow drift in downtown St. Louis on January 6.

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Winter weather grips U.S. – A man shovels the snow off his car in Indianapolis on January 6.

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Winter weather grips U.S. – A woman walks to the University of Minnesota's St. Paul campus on January 6.

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Winter weather grips U.S. – A man clears the sidewalk in front of his home in Carmel, Indiana, on January 6.

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Winter weather grips U.S. – A blanket of fog covers Lake Michigan along the Chicago shoreline January 6.

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Winter weather grips U.S. – A man braves the snow in downtown Springfield as a winter storm moves across the Midwest on Sunday, January 5.

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Winter weather grips U.S. – A car is buried in snow January 5 in Zionsville, Indiana.

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Winter weather grips U.S. – A city snowplow clears the street in an almost-deserted downtown Springfield on January 5.

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Winter weather grips U.S. – With the Gateway Arch in the distance, a person struggles to cross the street during a snowstorm January 5 in downtown St. Louis.

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Winter weather grips U.S. – Snow covers a garden gnome in St. Louis on January 5.

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Winter weather grips U.S. – Anna Maksimkina of Yekaterinburg, Russia, sleeps on the floor at John F. Kennedy International Airport in New York after a Delta flight from Toronto to New York skidded off the runway into a snow bank, temporarily halting all flights January 5.

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Winter weather grips U.S. – Four homeless men warm themselves on a steam grate by the Federal Trade Commission Building, blocks from the U.S. Capitol in Washington, as frigid temperatures grip the nation's capital on Saturday, January 4.

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Winter weather grips U.S. – People go sledding in Prospect Park in Brooklyn, New York, on January 4.

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Winter weather grips U.S. – Snow is piled high in front of a Home Depot in Boston on January 4.

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Winter weather grips U.S. – Sunlight beams through the windows of a building that caught on fire Friday, January 3, in Plattsmouth, Nebraska. The firefighters' water froze all over the building.

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Winter weather grips U.S. – Michael Stanton walks between houses covered with ice in Scituate, Massachusetts, on January 3.

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Winter weather grips U.S. – Pedestrians brave wind and snow as they cross New York City's Fifth Avenue on January 3.

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Winter weather grips U.S. – Snow clings to the clothing and facial hair of Jerome Williams as he uses a snowblower in front of his home in Roosevelt, New York, on January 3.

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Winter weather grips U.S. – Travelers wait in line January 3 at Chicago Midway International Airport.

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Winter weather grips U.S. – Frost covers the windows at the Morning Glory natural food store in Brunswick, Maine, on January 3.

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Winter weather grips U.S. – Snowplows clear snow from one of the runways at JFK Airport on January 3.

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Winter weather grips U.S. – Surfers make their way through snow on New York's Rockaway Beach on January 3.

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Winter weather grips U.S. – Passengers wait in line at a security checkpoint at JFK Airport on January 3.

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Winter weather grips U.S. – Blowing snow swirls as a worker shovels a platform at a Haddonfield, New Jersey, train station on January 3.

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Winter weather grips U.S. – A plane takes off January 3 as trucks plow snow at Newark Liberty International Airport in Newark, New Jersey.

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Winter weather grips U.S. – A man walks down a snowy road along the shore in Scituate on January 3.

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Winter weather grips U.S. – Postal worker Danny Kim clears snow and ice off the hood of his delivery truck January 3 in Bethesda, Maryland.

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Winter weather grips U.S. – A couple walks across a snow-covered parking lot January 3 at Newark Liberty International Airport.

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Winter weather grips U.S. – Tourists play in the snow at the base of the Washington Monument on January 3.

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Winter weather grips U.S. – People play in Brooklyn's Prospect Park on January 3.

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Winter weather grips U.S. – A man walks through the snow as the wind kicks it up January 3 in New York City.

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Winter weather grips U.S. – Dante de Blasio, son of New York Mayor Bill de Blasio, shovels snow outside his home in Brooklyn on January 3.

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Winter weather grips U.S. – Snow covers subway rails in New York City on January 3.

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Winter weather grips U.S. – A man uses his snowblower to clear some paths in Mansfield, Connecticut, on January 3.

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Winter weather grips U.S. – Workers clear snow off sidewalks on New York City's Fifth Avenue on January 3.

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Winter weather grips U.S. – A man clears snow from a vehicle January 3 in Albany, New York.

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Winter weather grips U.S. – A truck-mounted snowblower clears a section of road in Dedham, Massachusetts, on January 3.

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Winter weather grips U.S. – A worker clears snow from a subway station in Queens, New York, on January 3. Public schools were closed Friday after up to 7 inches of snow fell in New York City.

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Winter weather grips U.S. – A man shovels snow during the tail end of a snowstorm in Brooklyn on January 3.

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Winter weather grips U.S. – A man rides an all-terrain vehicle through a Brooklyn street on January 3.

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Winter weather grips U.S. – The Kunta Kinte-Alex Haley Memorial is covered in snow in Annapolis, Maryland, on January 3.

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Winter weather grips U.S. – A man plows snow January 3 following an overnight snowstorm in Jersey City, New Jersey.

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Winter weather grips U.S. – A child sleds down a hill in Chicago's Humboldt Park on Thursday, January 2.

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Winter weather grips U.S. – Children make a snow pile in New York's Times Square on January 2.

Winter weather grips U.S. – A man drags a suitcase on a snowy street in downtown Boston on January 2.

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Winter weather grips U.S. – A van is pulled from a ditch along Interstate 94 in Jackson, Michigan, on January 2.

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Winter weather grips U.S. – A man walks his dog on the snow-covered Monon Trail in Carmel, Indiana, on January 2.

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Winter weather grips U.S. – An airplane waits for passengers at O'Hare International Airport in Chicago on January 2.

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Winter weather grips U.S. – A woman walks through snowy conditions in Albany on January 2.

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Winter weather grips U.S. – Trucks clear snow off the roads in Torrington, Connecticut, on January 2.

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EXPAND GALLERY

The upper-level winds that make up the polar vortex change in intensity from time to time. When those winds decrease significantly, it can allow the vortex to become distorted, and the result is a jet stream that plunges deep into southern latitudes, bringing the cold, dense Arctic air spilling down with it. This oscillation is known as the Arctic Oscillation and it can switch from a positive phase to negative phase a few times per year. This oscillation -- namely the negative phase where the polar winds are weaker -- tends to lead to major cold air outbreaks in one or more regions of the planet.

Where on Earth can this happen?

The polar vortex can lead to major cold air outbreaks in any portion of the Northern Hemisphere -- North America, Europe and Asia. This will lead to cold snaps in multiple locations, though not always.

How dangerous is a polar vortex distortion as compared to a tornado or hurricane?

Completely different type of systems. A cold air outbreak caused by the polar vortex is much more widespread and lasts longer than a single storm. With the widespread drop in temperature, however, you can see significant winter storms develop, especially when the cold air is initially advancing into a previously warm region -- much like the nor'easter this past week.

When was the last big one to hit a denselypopulated area?

Serious cold snaps happen several times a year, though in different regions of the world and with different severities. Last March saw a significant decrease in temperature as a result of the polar vortex pushing into much of Europe. Many locations experienced an Easter holiday that was much colder than their Christmas holiday. The United Kingdom, for instance, had its coldest March in 50 years.

If you get caught up in one, what should you do?

Again, it's not a "storm" that you get caught in. But when faced with significant cold temperatures, you should stay inside whenever possible, layer clothing if you must be outside, winterize your home and car, etc.

Is it a side effect of global warming and should we expect more events like this?

This is a hotly researched topic. In short, yes, it could be. It seems counterintuitive that global warming could cause significant cold snaps like this one, but some research shows that it could. We know that different types of extreme weather can result from the overall warming of the planet, melting of the Arctic Sea ice, etc. This includes extreme distortions of the jet stream, which can cause heat waves in summer and cold snaps in winter.

Parts of Western Europe have been battered by the worst storms for two decades during the past week -- are they related to the weather system in the United States?

They are related in a sense, but I wouldn't say "caused by." The storms in Europe are the result of a persistent pattern that has seen the jet stream parked near the United Kingdom and Ireland, which has brought a train of storm systems over the British Isles. This is the same jet stream, of course, that has plunged deep into the southern portions of the United States. So, the jet stream has been "stuck" in a position that is allowing cold Arctic air to spill into much of the United States and Canada. But it is in a position that is bringing warmer, moist air from the Atlantic over Northwest Europe, resulting in the stormy conditions.